std: Add a net module for TCP/UDP

This commit is an implementation of [RFC 807][rfc] which adds a `std::net`
module for basic neworking based on top of `std::io`. This module serves as a
replacement for the `std::old_io::net` module and networking primitives in
`old_io`.

[rfc]: fillmein

The major focus of this redesign is to cut back on the level of abstraction to
the point that each of the networking types is just a bare socket. To this end
functionality such as timeouts and cloning has been removed (although cloning
can be done through `duplicate`, it may just yield an error).

With this `net` module comes a new implementation of `SocketAddr` and `IpAddr`.
This work is entirely based on #20785 and the only changes were to alter the
in-memory representation to match the `libc`-expected variants and to move from
public fields to accessors.

src/libstd/sys/unix/net.rs

@@ -0,0 +1,74 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use prelude::v1::*;
+
+use ffi;
+use io;
+use libc::{self, c_int, size_t};
+use str;
+use sys::c;
+use net::{SocketAddr, IpAddr};
+use sys::fd::FileDesc;
+use sys_common::AsInner;
+
+pub use sys::{cvt, cvt_r};
+
+pub type wrlen_t = size_t;
+
+pub struct Socket(FileDesc);
+
+pub fn init() {}
+
+pub fn cvt_gai(err: c_int) -> io::Result<()> {
+    if err == 0 { return Ok(()) }
+
+    let detail = unsafe {
+        str::from_utf8(ffi::c_str_to_bytes(&c::gai_strerror(err))).unwrap()
+            .to_string()
+    };
+    Err(io::Error::new(io::ErrorKind::Other,
+                       "failed to lookup address information", Some(detail)))
+}
+
+impl Socket {
+    pub fn new(addr: &SocketAddr, ty: c_int) -> io::Result<Socket> {
+        let fam = match addr.ip() {
+            IpAddr::V4(..) => libc::AF_INET,
+            IpAddr::V6(..) => libc::AF_INET6,
+        };
+        unsafe {
+            let fd = try!(cvt(libc::socket(fam, ty, 0)));
+            Ok(Socket(FileDesc::new(fd)))
+        }
+    }
+
+    pub fn accept(&self, storage: *mut libc::sockaddr,
+                  len: *mut libc::socklen_t) -> io::Result<Socket> {
+        let fd = try!(cvt_r(|| unsafe {
+            libc::accept(self.0.raw(), storage, len)
+        }));
+        Ok(Socket(FileDesc::new(fd)))
+    }
+
+    pub fn duplicate(&self) -> io::Result<Socket> {
+        cvt(unsafe { libc::dup(self.0.raw()) }).map(|fd| {
+            Socket(FileDesc::new(fd))
+        })
+    }
+
+    pub fn read(&self, buf: &mut [u8]) -> io::Result<usize> {
+        self.0.read(buf)
+    }
+}
+
+impl AsInner<c_int> for Socket {
+    fn as_inner(&self) -> &c_int { self.0.as_inner() }
+}